ORIGINAL: f2racer
A MVVS 40 equipped with a mini-tuned pipe and an APC 11x4 prop is a killer setup. I had one on my Knife ARF and it hovered at about 2/3 throttle. On a lightweight kit-built Sledge (which would likely be a full pound lighter than my ARF), the engine would be even more impressive.
You must have a bad a** MVVS 40 or either a really light Knife ARF. I tried that same combo and ended up with an Irvine 53 to get my fat Knife ARF to hang.
My suggestion would be the Irvine since mine has pefromed flawlessly....maybe an oz or two heavier but power out the wazoo. But I hear that even a TT46pro or OS46FX will handle a kit built profile providing its around the 4lb range. Remember...can never have too much power but the weight is always equally imprtant.